Lubricant composition



United States Patent "ice 3,150,093 LUBRICANT COMPOSITION Daniel B. Eickemeyer, Park'Forest, 111., and James E.

Engellring, St. Paul, Minn., assignors, by mesne assignments, to Sinclair Research, Inc., New York, N.Y., a corporation of Delaware 7 No Drawing. Filed June 9, 1960, Ser. No. 34,892

4 Claims. (Cl. 25246.3)

This invention relates to ester-based lubricant compositions containing a novel combination of additive agents. More particularly the present invention relates to ester-based lubricant compositions which exhibit increased oxidation resistance.

Organic compounds, such as lubricating oils, undergo oxidation upon exposure to air. This proceess as accentuated by elevated temperatures such as occur in engines and other operating machinery. When such. organic compositions are used as motor or machinery lubricants, their stability is still further drastically reduced due to their contact with metal surfaces which give up metallic particles into the lubricant. Such abraded or dissolved metals or metal salts appear to act as oxidation catalysts in the lubricant causing the formation of primary oxidation products which in turn cause further degradation of the organic compounds present in the composition. In addition, water also causes corrosion of metallic surfaces and accentuates oxidation of the lubricant. Problems of this nature are encountered in mineral oils but appear to be particularly troublesome in synthetic oleaginous fluids exemplifiedby esters. These synthetic fluids are not suffic iently resistant to oxidation to be usefulralone. They can, however, be adequately protected by use of small amounts of additives. Phenothiazine has been employed extensively to protect synthetic fluids against oxidation. Its activity, however, is not great enough to protect fluids for long periods of time above about 400 F. I

It is the particularobject of the present invention to provide an ester oil of lubricating viscosity that exhibits increased resistance to oxidation. Further, the additives of the present invention have proven far more effective than the conventional use of phenothiazine alone in reducing oxidation in synthetic ester fluids.

The present invention provides an improved ester-based lubricant composition containing minor amounts effective to retard oxidation, of phenothiazine, -alkyl-10,10-diphenylphenazasiline wherein the alkyl group is a lower alkyl group, i.e. generallyof about 14 carbon atoms, preferably 2 carbon atoms and a compound selected from the group consisting of aminoquinoline, aminopyridine and their mixtures.

The rings of the siline compound may be substituted as for instance with alkyl groups. The additives of the 1 present invention are added in amounts that provide a final ester-based synthetic lubricant composition exhibiting increased resistance to oxidation under temperatures such as in excess of 400 F. The amounts added should be soluble in the base oil into which .they are introduced and these amounts Will vary with the particular base oil utilized. g

Thepreferred aminoquinolines for use in thepresent invention are 3-aminoquino1ine and S-aminoquinoline and.

their ring substituted derivatives, e.g. alkyl-substituted. Among the useful aminopyridines are 2-aminopyridine and the ring-substituted, e.g. alkyl substituted, aminopyridinesv The-aminoquinoline or aminopyridine may be added in. amounts from about .015% by weight of final composition with-a preferred amount of from about 0.1 to 2% by weight of final composition. The aminoquinoline or aminopyridine and the 5-alkyl-10,10-diphenylphenazasiline additive are normally added to the esteraforementioned,

3,15,093 Patented Sept. 22, 1964 based by lubricant along the phenothiazine. The phenothiazine is usually present in amounts from about .01-5% by weight of the final composition with a preferred amount being from about 0.12% and the phenothiazine may be substituted as with alkyl groups, for instance on the nitrogen or in positions ortho and meta to the nitrogen. The 5-alkyl-10,IO-diphenylphenazasiline component is generally added in amounts of about .015% by weight of the final composition with a preferred amount of from about 0.1 to 2% by weight of final composition. As the preferred diphenylphenazasiline component is S-ethyl-ltl,10-diphenylphenazasiline. For obtaining best results, the relative concentrations of the additives may vary with the particular ester lubricant employed and may also be dependent upon the characteristics of the final lubricant composition desired. Normally it is preferred that at least about 1 part of S-alkyl- 10,IO-diphenylphenazasiline and at least about 0.5 part of aminoquinoline or aminopyridine to one part of phenothiazine be utilized, e.g. about 1-2.5 parts 5-alkyl-10,10- diphenylazasiline and about 0.5-1.5 aminoquinoline. or aminopyridine to one part of phenothiazine. Increasing the amounts of S-alkyl-IO,10-diphenylphenazasiline and aminoquinoline or aminopyridine will generally be desired.

The lubricant composition of this invention includes as the major compound a base oil which is an ester of lubricating viscosity which may be, for instance, a simple ester or compounds having multiple ester groupings such as complex esters, polyesters, or diesters. These esters are made from monoand polyhydroxy aliphatic alcohols and aliphatic carboxylic acids, frequently of about 4 to 12 carbon atoms; aliphatic including cycloaliphatic. The reaction product of a monohydroxy alcohol and a monocarboxylic acid is usually considered to be a simple ester. A diester is usually considered to be the reaction product of 1 mole of a carboxylic acid, say of 6 to 10 carbon atoms, with 2 moles of a monohydric alcohol or of 1 mole of a glycol of 4 to 10 carbon atoms with 2 moles of a monocarboxylic acid of 4 to 10 carbon atoms. The diesters frequently contain from about 20 to carbon esters, wherein X represents a monoacid residue, Y represents a glycol residue and Z represents a dibasic acid residue are also considered to be complex esters. The complex esters often have 30 to 50 carbon atoms. or polyester bright stocks can be prepared by direct esterification of dibasic acids with glycols in about equimolar quantities. The polyesterification reaction is usually continued until the product has a kinematic viscosity from about 15 to 200 centistokes at 210 F., and preferably 40 to 13 0 centistokes at 210 F.

Although each of these products in itself is useful as a lubricant, they are particularly useful when added or blended with each other in synthetic lubricant compositions. These esters and blends have been found to be especially adaptable to the conditions to which turbine engines are exposed, since they can be formulated to give a desirable combination of high flash point, low pour point, and high viscosity at elevated temperatures, and need contain no additives which might leave a residue upon volatilization. In addition, many complex esters have shown good stability to shear. Natural esters, such as castor oil may also be included in the blend as may be up to about 1 percent or more by Weight of a foam inhibitor such as a methyl silicone polymer or other additives to provide a' particular characteristic, for instance, extreme pressure or load carrying agents, corrosion inhibitors, etc., can be added.

Polyesters,

Typical synthetic lubricants may be formulated essentially from a major amount (about 60-85%) of a complex ester and a minor amount (about 1540%) of a diester, by stirring together a quantity of diester and complex ester at an elevated temperature, altering the proportions of each component until the desired viscosity is reached. Polyesters can be employed to thicken diester base stocks to increase the load carrying capacity of the base diester oil. The polyester will generally not comprise more than about 50 weight percent of the blend, preferably about 20 to 35 weight percent. Usually the amount of the polyester employed in any blend would be at least about 3 percent, and the majority of the lubricant is a diester. Other polymers such as acryloids may be added as thickeners to the esters, generally the single esters such as the above diesters, to obtain a base oil of desired viscosity. The acryloids are polymers of mixed C to C esters of methacrylic acid having 10,000 to 20,000 molecular weight. Advantageously the final lubricating oil composition would have a maximum viscosity at -40 F. of about 13,000 centistokes and a minimum viscosity of about 7.5 centistokes at 210 F.

The monohydric alcohols employed in these esters usually contain less than about 20 carbon atoms and are generally aliphatic. Preferably the alcohol contains up to about 12 carbon atoms. Useful aliphatic alcohols include butyl, hexyl, methyl, iso-octyl, and dodecyl alcohols, C oxo alcohols and octadecyl alcohols. C to C branched chain primary alcohols are frequently used to improve the low temperature viscosity of the finished lubricant composition. Alcohols such as n-decanol, 2-ethylhexanol, oxo alcohols, prepared by the reaction of carbon monoxide and hydrogen upon the olefins obtainable from petroleum products such as diisobutylene and C olefins, ether alcohols such as butyl carbitol, tripropylene glycol mono-isopropyl ether, dipropylene glycol mono-isopropyl ether, and products such as Tergitol 3A3, which has the formula are suitable alcohols for use to produce the desired lubricant. If the alcohol has no hydrogens on the beta carbon atoms, it is neo-structured; and esters of such alcohols are often preferred. In particular, the nee-C alcohol-2,2,4-trimethyl-pentanol-1gives lubricating diesters or complex esters suitable for blending with dieste rs to produce lubricants which meet stringent viscosity requirements. Iso-octanol and iso-decanol are alcohol mixtures made by the oxo process from C -C copolymer heptenes. The out which makes up iso-octanol usually contains about 17% 3,4-dimethylhexanol; 29% 3,5-dimethylhexanol; 25% 4,5-dimethylhexanol; 1.4% 5,5-dimethylhexanol; 16% of a mixture of 3-methylheptanol and S-ethylheptanol; 2.3% 4-ethylhexanol; 4.3% a-alkyl alkanols and other materials.

Generally, the glycols contain from about 4 to 12 carbon atoms; however, if desired they could contain a greater number. Among the specific glycols which can be employed are 2-ethyl-1,3-hexanediol, 2-propyl-3,3- heptanediol, 2-methyl-1,3-pentanediol, 2-butyl-l,3-butanediol, 2,4-dipheny1-1,3-butanediol, and 2,4-dirnesityl-1,3- butanediol. In addition to these glycols, ether glycols may be used, for instance, where the alkylene radical contains 2 to 4 carbon atoms such as diethylene glycol, dipropylene glycol and other glycols up to 1000 to 2000 molecular weight. The most popular glycols for the manufacture of ester lubricants appear to be polypropylene glycols having a molecular weight of about 100-300 and 2-ethyl hexanediol. The 2,2-dimethyl glycols, such as neopentyl glycol have been shown to impart heat stability to the final blends. Minor amounts of other glycols or other materials can be present as long as the desired properties of the product are not unduly deleteriously affected.

Aside from glycols, the esters may be made from polyhydric alcohols of more than two hydroxyl groups, e.g. triand tetrahydroxy aliphatic alcohols having about 4 to 12 carbon atoms preferably about 5 to 8 carbon atoms, for instance pentaerythritol, trimethylolpropane and the like. Particularly suitable ester base oils are formed when these alcohols are reacted with monocarboxylic acids having about 4 to 12 carbon atoms, preferably 4 to 9 carbon atoms. It is preferred that the reaction be conducted so as to substantially completely esterify the acids.

One group of monocarboxylic acids includes those of 8 to 24 carbon atoms such as stearic, lauric, etc. The carboxylic acids employed in making ester lubricants will oftencontain from about 4 to 12 carbon atoms. Suitable acids are described in U.S. Patent No. 2,575,195, and include the aliphatic dibasic acids of branched or straight chain structures which are saturated or unsaturated. The preferred acids are the saturated aliphatic carboxylic acids containing not more than about 12 carbon atoms, and mixtures of these acids. Such acids include succinic, adipic, suberic, azelaic, and sebacic acids and isosebacic acid which is a mixture of a-ethyl suberic acid, c d-diethyl adipic acid and sebacic acid. This composite of acids is attractive from the viewpoint of economy and availability since it is made from petroleum hydrocarbons rather than the natural oils and fats which are used in the manufacture of many other dicarboxylic acids, which natural oils and fats are frequently in short supply. The preferred dibasic acids are sebacic and azelaic or mixtures thereof. Minor amounts of adipic used with a major amount of sebacic may also be used with advantage.

Various useful ester base oils are disclosed in United States Patents Nos. 2,499,983, 2,499,984, 2,575,195, 2,- 575,196, 2,703,811, 2,705,724 and 2,723,286. Generally, the synthetic base oils consist essentially of carbon, hydrogen and oxygen, i.e. the essential nuclear chemical structure is formed by these elements alone. However, these oils may be substituted with other elements such as halogens, e.g. chlorine and fluorine. Some representative components of ester lubricants are ethyl palmitate, ethyl stearate, di-(2-ethylhexyl) sebacate, ethylene glycol di-laurate, di-(Z-ethylhexyl) phthalate, di- (1,3 -methyl butyl) adipate, di-(Z-ethyl butyl) adipate, di-(l-ethyl propyl) adipate, diethyl oxylate, glycerol tri-n-octoate, di-cyclohexyl adipate, di-(undecyl) sebacate, tetraethylene glycol-di-(Z-ethylene hexoate), dicellosolve phthalarte, butyl phthallyl butyl glycolate, di-n-hexyl fumarate polymer, dibenzyl sebacate, and diethylene glycol bis (2-nbutoxy ethyl carbonate). 2-ethylhexyl-adipate-neopentyl glycyl-adipate-2-ethylhexyl, is a representative complex ester. Generally, these synthetic ester lubricants have a viscosity ranging from light to heavy oils, e.g. about 50 SUS at F. to 250 SUS at 210 F., and preferably 30 to SUS at 210 F.

The esters are manufactured, in general, by mere reaction of the alcoholic and acidic constituents, although simple esters may be converted to longer chain components by transesterification. The constituents, in the proportions suitable for giving the desired ester, are reacted preferably in the presence of a catalyst and solvent or water entraining agent to insure maintenance of the liquid state during the reaction. Aromatic hydrocarbons such as xylene or toluene have proven satisfactory as solvents. The choice of solvent influences the choice of temperature at which the esterification is conducted; for instance, when toluene is used, a temperature of 140 C. is recommended with xylene, temperatures up to about C. may be used. To provide a better reaction rate an acid esterification catalyst is often used. Many of these catalysts are known and include, for instance, HCl, H SO NaHSO aliphatic and aromatic sulfonic acids, phosphoric acid, hydrobromic acid, HF and dihydroxy fluoboric acid. Other catalysts are thionyl chloride, boron trifiuoride, and silicon tetrafluoride.

Titanium esters also make valuable esterification and transesterification catalysts.

In a preferred reaction, about 0.5 to about 1 weight percent, or advantageously, 0.2 to 0.5% of the catalyst 6 The lengths of the induction periods serve as a significant measure of the relative effectiveness of the inhibitors. As shown in Table I addition of the novel additive combination of the present invention protects the fluid against is used with a xylene solvent at a temperature of 165 to rapid oxidation for a longer period of time than would 200 C. while refluxing water. The temperatures of the be expected if the effect were simply additive. reaction must be sufiicient to remove the water from the Other examples of formulations made in accordance esterification mass as it is formed. This temperature is with the present invention are as follows: usually at least about 140 C. but not so high as to de- 7 compose the wanted product. The highest temperature 10 EXAMPLE I Parts b w needed for the reaction will probably be about 200 C., 1 y

o Plexol-201 97.5 preferably not over about 175 C. The pressure is con- Titaniu 2 m polymer 1.0 vemently about atmospheric. Although reduced pressure Phenothiazine 0 5 or super-atmospheric pressure could be utilized, there is 5 ethy1 10,lodiphenylphenazasfline L0 usually no necessity to use reduced pressures, as the tem- 5 Laminopyridine 0 5 peraltures required at atmospheric pressure to remove the D C F O 60 6' oool water formed do not usually unduly degrade the product. th 1h e .lbt'lh' k t"'t when we glxwls wlth dlbeslc to q if as assassin a polyester, 1t 1s preferred to continue the reaction with of below 80 F. and acid No. of 0.12. concomitant boiling ofl of water from the reaction mix- 20 1 f gg gf denved fmm tetmbutyl titanate and z-s ture until the polyester product has a kinematic viscosity D.C.F. 200'-e0,o00 is a methyl silicone polymer having a of about 15 to 200 oentistokes at 210 F, Preferably viscosity of 60,000 cs. at C. and is an anti-foaming agent. about 40 to 130 centistokes. When this point has been EXAMPLE reached, the polymerization can be stopped, for instance, Parts by Wt. by adding a capping alcohol to the reaction mixture, 25 P c 55 1 98.75 and continuing to reflux until water ceases to be evolved. Phenothiazine 0.5 The capping alcohol is a low molecular weight mono Glycol titanate 2 l 0.25 alcohol of up to about 20 carbon atoms. It is standard j-ethyl-l0,IO-diphenylphgnazasiline 1 0 practice, when esters are made using the conventional 2 i i i 5 acid catalysts such as sodium bisulfate or paratoluene- Sebacic acid 0075 sulfomc acid to give the esters an after-treat by washing 200 60 000 001 the ester with a 5 percent aqueous K CO solution or 1A t d" t t I b t d mlX ure 0 11800 a l a e, 1 1'1 C 3C3. e, an by heamng ester m autoclave for 15 hours at 2 Acryloid-966 (a copolymeb: of al iryl with acfiyl itte s and N-vinyl to 350 F. with 10 weight percent of propylene oxide. py rrolidone). It is also conventional to subject the ester to filtration .to Polymer of tltamum tetrwalkyl esters and glycol remove insoluble materials. After this the product may EXAMPLE III be subjected to a reduced pressure distillation or stripping Parts by wt. at 100 to 200 C. to remove volatile materials, such as Diisooctyl azelate 25.5 water, the solvent, and light ends. (3 h ester 1 74 Samples of ester fluids without an oxidation inhibitor 40 Phenothiazine 5 and samples containing phenothiazine alone, 5-ethy1 Free azelaic acid m1 loalo'dlphenylphenazaslhne pheqathlazme and 5-ethyl-10,lo-diphenylphenazasifine 1,0 aminopyridine and samples made according to the present zaminopyridina 0.5 invention were subjected to oxygen absorption tests. The D C F 2O0 60 000 (L001 tests were conducted at 450 F. by passing a stream of oxygen at the we f 1 wbsfwt e 75 2 1.331%??? assassins that; assassinat grams of the ester fluid containing the inhibitors and comparing the amount of oxygen absorbed vs. time. The In the composit ons of Table I and of Examples I, II, induction period is signalled by a marked increase of and IIL PY f replaced W1th oxygen absorption. The results of these tests are shown Parts by weight of 3-aminoqu1nol1ne and obtam essenin Table I. tially the same results.

TABLE I Results of Oxygen Absorption Tests [Conditionsz 450 F.;1 it. Or/hn; g. fluid] Conc Induction Total Volume Run No. Base Additives (wt. period time a fluid percent) (min) (m1n.) absorbed 5 119 a, 000 i 30 800 0.5 117 146 2, 130.-- do d 205 247 2, 500 253 d0 {Hm-mpyridmm 305 351 2,500

ghenothiazinre 0 5 -B.IH1HO 1 me 313 S-ethyl-IifiO-diphenylphenazasiline. 15s .-do 5-ethyl-10,l0-diphenyl- 1.0 5 47 2,500

1 Pl i ifgh iz z ib -eth 1- 304 18,10-diphenyly Q 3 s19 ass 2, 500

phenazasiline.

1 An ester from pentaerythritol and a mixture of aliphatic acids with an average chain length of seven carbons.

however.

We claim:

1. A lubricant composition consisting essentially of an ester-based fluid of lubricating viscosity and minor amounts effective to retard oxidation of said ester-based fluid at temperatures in excess of 400 F., of about .01 to 5 percent by Weight of phenothiazine, about .01 to 5 percent by weight of 5-alkyl-10,IO-diphenylphenazasiline wherein the alkyl group contains 1 to 4 carbon atoms, and about .01 to 5 percent by weight of a compound selected from the group consisting of aminoquinoline and aminopyridine, said ester-based fluid being an ester of an alkanol of 4-10 carbon atoms and an alkane carboxylic acid of 4-12 carbon atoms.

2. The composition of claim 1 wherein the compound selected is aminopyridine.

3. The composition of claim 1 wherein the compound selected is aminoquinoline.

4. The lubricant composition of claim 1 containing about 0.1 to 2 percent by Weight of phenothiazine, about 0.1 to 2 percent by weight of 5-ethyl-10,10-diphenylphenazasiline and about 0.1 to 2 percent by Weight of a material selected from the group consisting of 2-aminopyridine and 3-arninoquinoline.

References Cited in the file of this patent UNITED STATES PATENTS 2,216,711 Musher Oct. 1, 1940 2,318,196 Chenicek May 4, 1943 2,950,250 Fainman Aug. 23, 1960 3,036,005 Kock May 22, 1962 3,038,858 Verley June 12, 1962 3,038,859 Eickerneyer et al June 12, 1962 OTHER REFERENCES 

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF AN ESTER-BASED FLUID OF LUBRICATING VISCOSITY AND MINOR AMOUNTS EFFECTIVE TO RETARD OXIDATION OF SAID ESTER-BASED FLUID AT TEMPERATURES IN EXCESS OF 400*F., OF ABOUT .01 TO 5 PERCENT BY WEIGHT OF PHENOTHIAZINE, ABOUT .01 TO 5 PERCENT BY WEIGHT OF 5-ALKYL-10,10-DIPHENYLPHENAZASILINE WHEREIN THE ALKYL GROUP CONTAINS 1 TO 4 CARBON ATOMS, AND ABOUT .01 TO 5 PERCENT BY WEIGHT OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF AMINOQUINOLINE AND AMINOPYRIDINE, SAID ESTER-BASED FLUID BEING AN ESTER OF AN ALKANOL OF 4-10 CARBON ATOMS, AND AN ALKANE CARBOXYLIC ACID OF 4-12 CARBON ATOMS. 